Magnetogenerator



Sept. 27, 1949. M. c. SAWYER memz'ro GENERATOR Filed June 30, 1944INVENTOR.

HTTORNEY Patented Sept. 27,1949

2,482,875 MAGNETOGENEMTOB Marc 0. Sawyer, Otsego County, N. Y., assignorto Bendix Aviation Corporation, New York, N. Y., a corporation ofDelaware Application J line 30, 1944, Serial N0. 542,908

This invention relates to electrical apparatus and more particularly toignition means for internal combustion engines and current generatingmeans therefor.

- One of the objects of the present invention is to provide a novelsource of unidirectional electrical current which is adapted for use inignition systems for internal combustion engines, or the like.

Another object of the invention is to provide novel current generatingmeans which is suitable as a source of current in a condenser dischargetype of ignition circuit.

Still another object is to provide a novelly constructedmagnetogenerator which has suitable voltage output characteristics tomake it adaptable for use in an internal combustion engine ignitionsystem.

A further object is to provide novel current generating apparatus .whichhas good voltage regulation characteristics over a wide range of speeds.

A still further object is to providenovel apparatus of the abovecharacter which is selfcontained and independent of any outsideelectrical source for excitation.

The above and further objects and novel features of the invention willmore fully appear from the following detailed description when the sameis read in connection with the accompanying drawing. It is to beexpressly understood, however, that the drawing is for the purpose ofillustration only and is not intended as a definition of the limits ofthe invention, reference for this latter purpose being had primarily tothe appended claims.

The single figure of the accompanying drawing is a diagrammaticillustration of one form of magnetogenerator comprehended by theinvention and shown in connection with one type of ignition circuit inwhich it is particularly advantageous.

The only embodiment of the invention shown in the drawing, by way ofexample, is in the form of a two-pole magnetogenerator which isparticularly suitable for use in supplying electrical energy for aninternal combustion engine ignition system of the type hereinafterdescribed. As illustrated, the generator may comprise an armature orrotor provided with a plurality of windings 6 connected to a commutatorl. The above parts of the contemplated structure may be constructed ofany suitable materials and in any suitable manner well understood in theart.

The armature 5 may be driven by the engine 5 Claims. (01. 3221-50) onwhich the ignition system is installed, the speed ratio between thecrankshaft and the armature being dependent upon the size of thegenerator in relation to the desired voltage at, all engine speeds.

Ordinarily, it is desirable in aircraft to use the smallest generatorwhich can be relied upon to supply the desired voltages at safeoperating speeds. In one suitable system, the armature isdriven at aboutthree times crankshaft speed to obtain the desired voltage at idling andfull speed. As the armature rotates in a magnetic field to behereinafter described, current is generated in windings 6. This currentis picked up from the commutator 1 and delivered as unidirectionalcurrent to a circuit by a pair of brushes 8 and 9 in a manner wellunderstood in the art. As shown, brush 8 is connected by lead It toground and brush 9 is connected by a lead II 'to the remainder of anignition circuit.

In order that the magnetic field and, hence, the magnetic fiuxthrougharmature 5 will be a maximum at zero speed, this field is created by oneor more permanent magnets interposed between a pair of pole shoes l2mounted adjacent to and on opposite sides of the armature. The poleshoes are preferably of laminated magnetic steel. In the'form shown, abar magnet l4 engages each pole shoe H, the same being arranged so thatthe north pole of one magnet engages one pole shoe and the south pole ofthe other magnet engages the other pole shoe. The other opposite polesof the magnets may be magnetically connected in any suitable manner,such as by a magnetic flux conducting member l5 which may be the housingof the generator.

In the operation of the structure thus far de scribed, the voltageoutput of the generator will increase substantially as the speed of thearmature increases. Novel means are accordingly provided for the purposeof materially reducing the maximum voltage output of the generator andyet insure the necessary voltage output at low or idling speeds and alsominimize the change or variation in voltage output over a wide speedloadrange. Said means, as shown, comprises a shunt for the magnetic field ofeach magnet ll.

This shunt, in the illustrated structure. is accomplished by extendingprojections 16, It from the pole shoes l2 into air gap relation withmember l5 to form an alternate or shunting flux path. The exact natureof the shunt will, of course, vary in differently constructedgenerators;

In order to vary the proportionate amount of the magnetic flux whichflow in the main flux aseaavs path through the armature and in the shuntpaths thus formed in accordance with the speed of the armature, acompensating or bucking field is created by means of coils l1, l1 woundon pole shoes l2, l2. These coils are preferably but not necessarilyconnected in series across the output terminals or brushes 8, 9 of thegenerator and so connected that the magnetic field set up around thesame by the flow of current therethrough bucks the flow of magnetic fluxfrom the magnets l4, l4 through the pole shoes l2, l2 and armature 5. Ineffect, the bucking coils increase the reluctance of the main magneticflux path and causes a larger percentage of the flux from the magnets tofiow in the shunt paths. The effect of the bucking coils increases withspeed because the current generated increases with armature speed.

The required number of turnsin each of coils I1 and the requiredreluctance of the shunting flux paths will vary in different systemsdepending on the results desired. In one practical em- .bodiment inwhich a voltage output of 300 volts was obtained at engine idling speedand about 450 volts at maximum speed-load conditions, 2000 .turns of No.40 wire were used in each coil. This voltage range could be furtherreduced if necessary by properly proportioning the reluctance of theshunt and main flux paths. This may be done, for example, by changingthe size of the air gap at the ends of projections Hi, i. e., in theshunting flux path, the cross sectional area of said projections or thecharacter and size of coils IT.

The novel magneto generator thus comprehended is shown, by way ofexample only, as being connected in an ignition circuit wherein adischarge condenser l8 of approximately onehalf microfarad' capacity isoperatively connected across terminals 8, 9, one side of the condenserbeing connected to ground and the other to brush 9. The ungroundedterminal of condenser I8 is connected to a terminal of a circuitcontactor IS,

the movable contact of which may be periodically moved in one directionby suitable resilient means and in the other direction b means such as arotating cam in a manner well understood in the art. The other terminalof the contactor is connected .to the end of the primary winding 20 of ahigh frequency transformer, the secondary winding 2| of which isconnected in series with a spark plug 22.

Thus, when contactor I9 is open, condenser 18 will be charged by thegenerator. The primary circuit including the condenser, contactor andwinding 20 is periodically closed at times when the condenser ischarged, thereby permitting a high frequency discharge from thecondenser through the primary winding. The rise and fall of theoscillating current in the primary winding causes current to be inducedin Winding 2| at a sufiiciently high voltage to create sparks across thegaps of spark plug 22. The maximum voltage output of the generator iskept at a relatively low value, such as 450 [to 500 volts, to preventarcing and, hence, unnecessary dissipation of energy at the contactorpoints as well as to prevent deterioration of said points. The generatormust be designed, however, to provide ample voltage at idling speed. Thevoltage output range may be varied but a minimum of about 300 volts atengine idling speed permits the use of a relatively small transformercoil 20, 2| which may be readily incorporated in a radio shielded sparkplug.

In a multi-cylinder engine, a plurality of par- 4 allel connectedcontactors each in a circuit with a transformer 20, 2| may be employed,as illustrated, means being provided for operating the contactors intimed sequence. If desired, however, one contactor and a suitabledistributor may beprovided.

There is thus provided novel simplified ignition apparatus embodying anovelly constructed current generating means whereby a relatively smallrange of voltage output is obtained between maximum and idling enginespeeds. The novel generator provided renders feasible and practical alow voltage distribution, high frequency ignition system wherein thedanger of ignition failures at all altitudes is reduced to a minimum, asare also the radio shielding requirements of the system.

Although only a single embodiment of the invention is illustrated in theaccompanying drawings and described in the foregoing specification, itis to be expressly understood that the same is not limited thereto. Forexample, the generator may be employed in various other ignition systemsor the like and other types of current generating means may be employedin the ignition circuit shown. Various other changes may also be madeparticularly in the design and arrangement of parts illustrated and inthe electrical values and materials mentioned above, by way of example,without departing from .the spirit and scope of the invention as thesame will now be understood by those skilled in the art. For adefinition of the limits of the invention, reference is had primarily tothe appended claims.

What is claimed is:

1. In apparatus of the class described, a magnetic flux conducting rotorhaving windings thereon, a commutator operatively connected with saidwindings, a plurality of stationary pole shoes adjacent said rotor,permanent magnet means associated with said pole shoes whereby magneticflux from said magnet means is caused to flow through said pole shoesand rotor, means shunting some of said magnetic flux away from saidrotor, and means for decreasing the magnetomotive force across thearmature magnetic circuit, said last-named means including a coil woundon each of said pole shoes and means including said commutator forelectrically connecting said coils to said armature windings so that themagnetic fields set up by the flow of current through said coils tendsto counteract the flow of magnetic flux to said rotor from said magnetmeans.

2. A magnetogenerator comprising a plurality of magnets having unlikepoles connected by a flux conducting member, pole shoes connected withsaid magnets, a variable speed armature between said shoes, said shoesand armature being adapted to carry the magnetic flux, a shunt extendingfrom a position between the magnets and shoes into flux conductingrelation to said flux conducting member, and bucking coils between theshunt and the armature adapted for excitation by the generator wherebythe proportion of flux deflected through the shunt may be increased asthe speed of the generator increases.

3. A magnetogenerator comprising a plurality of magnets having unlikepoles connected by a flux conducting member, pole shoes connected withsaid magnets, a variable speed armature between said shoes, said shoesand armature being adapted to carry the magnetic flux, a shunt extendingfrom a position between the magnets and shoes into flux conductingrelation to said i'lux conducting member, and means between the shuntand the armature adapted for excitation by the generator whereby theproportion of flux deflected through the shunt may be increased as thespeed of the generator increases.

4. A magnetogenerator having magnets with unlike magnetic polesconnected byaflux con ducting member, pole shoes and a variable speedarmature adapted to carry the magnetic flux, a shunt extending from aposition between the magnets and shoes into flux conducting relation tosaid flux conducting member; and means adapted to be excited'by. thegenerator to deflect an increasing proportion of flux through the shuntas the speed of the generator increases.

5. In apparatus of the class described a generator having a plurality ofmagnets with unlike poles connected by a flux conductor, pole shoesconnected to the other poles of said magnets, a, variable speed armaturepositioned between the said pole shoe, and an interrupted fluxconducting 'shunt circuit between the poles of each magnet and the poleshoes, and bucking coils in between the armature and, said shuntcircuits, supplied with current from the armature to divert flux fromthe armature to the shunt circuits.

' MARC C. SAWYER.

REFERENCES CITED The followingre'ferences are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,024,225 Remy eta1. Apr. 23,1912 1,527,641 Gilt Feb, 24, 1925 1,531,389 Gordon e- Mar. 31, 19251,622,145 Hunt Mar. 22, 1927 1,962,691 Landis June 12, 1934' FOREIGNPATENTS Number Country Date 20,225 Great Britain ......h..... 1912176,091- Switzerland June 1'7, 1935

